This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. This research is studying the change in the level of vitamin D in the blood in response to peoples daily exposure to sunlight. Ultraviolet rays from the sun are known to stimulate the body to produce the active form of vitamin D which serves many functions necessary to our health. It is also known that exposure to sunlight is directly related to the development of certain types of skin cancer. Although vitamin D can be found in certain foods and dietary supplements, it has been argued that the vitamin D produced by sunlight is essential to maintaining healthy levels in our bodies. There are no previous studies measuring the amount of vitamin D that is produced by our bodies in response to a measured quantity of ultraviolet light from the sun. To date, there are only estimated amounts of sunlight that are considered necessary to obtaining specific amounts of vitamin D. This study will provide data that can more accurately demonstrate how much vitamin D is produced in the body in response to everyday exposure to the sun. It may then be possible to recommend minimal exposure to sunlight that adequately increases levels of vitamin D while avoiding excessive exposure times that increase the risk of skin cancer.